我怎样才能写一个正则表达式（regex）来排除US和USA这两个词？

Question

I have a form on my website that a form field for COUNTY. People routinely misread this as COUNTRY and end up putting into the field US or USA.

Is there regex that I can use to exclude the words:

US USA us usa

Thank you.

I searched the internet to see if this has been asked before and it has not been from what I can tell. I don't know how to write regex or expressions either though.

Answer 1

Use a negative lookahead to exclude a word.

Match US optionally followed by A .

 <form> County: <input type="text" pattern="(??[Uu][Ss][Aa].$).*"> </form>